Quantum dot-sensitized hierarchical micro/nanowire architecture for photoelectrochemical water splitting.

We report the fabrication of quantum dot-sensitized hierarchical structure and the application of the structure as a photoanode for photoelectrochemical water splitting. The structure is synthesized by hydrothermally growing ZnO nanowires on silicon microwires grown with the vapor-liquid-solid method. Then the hierarchical structure is further sensitized with CdS and CdSe quantum dots and modified with IrOx quantum dots. As a result, the silicon microwires, ZnO nanowires, and the quantum dot/ZnO core/shell structure form a multiple-level hierarchical heterostructure, which is remarkably beneficial for light absorption and charge carrier separation. Our experimental results reveal that the photocurrent density of our multiple-level hierarchical structure achieves a surprising 171 times enhancement compared to that from simple ZnO nanowires on a planar substrate. In addition, the photoanode shows high stability during the water-splitting experiment. These results prove that the quantum dot-sensitized hierarchical structure is an ideal candidate for a photoanode in solar water splitting applications. Importantly, the modular design approach we take to produce the photoanode allows for the integration of future discoveries for further improvement of its performance.